Remove the kDNSServiceInterfaceIndexLocalOnly special-case on Darwin.

[bzbarsky-apple]

Interface kDNSServiceInterfaceIndexLocalOnly means the registration is local-only, not that the registered host is localhost and has a loopback address. There can be local-only registrations for other hosts, and we need to do actual address resolution.

To make this work right in our unit test setup, fix our registration code for the local-only case (which tests use) to register hostname -> IP mappings, which it was not doing before.

[bzbarsky-apple]

@cecille This looks like it might reintroduce #11891, but I'd really like to understand exactly what was happening there and whether it still happens on tip + this PR... The networking folks tell me that there's nothing that should be special about the local-only interface here.

[github-actions]

PR #26287: Size comparison from e4d000d to f2654f7

Increases (1 build for cc32xx)

platform	target	config	section	e4d000d	f2654f7	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	19521971	19521973	2	0.0

Full report (1 build for cc32xx)

platform	target	config	section	e4d000d	f2654f7	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	602714	602714	0	0.0
			(read/write)	204156	204156	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197568	197568	0	0.0
			.comment	206	206	0	0.0
			.data	1468	1468	0	0.0
			.debug_abbrev	956984	956984	0	0.0
			.debug_aranges	103664	103664	0	0.0
			.debug_frame	350552	350552	0	0.0
			.debug_info	19521971	19521973	2	0.0
			.debug_line	2682751	2682751	0	0.0
			.debug_line_str	513	513	0	0.0
			.debug_loc	33340	33340	0	0.0
			.debug_loclists	1506147	1506147	0	0.0
			.debug_ranges	4984	4984	0	0.0
			.debug_rnglists	96278	96278	0	0.0
			.debug_str	3059490	3059490	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	104250	104250	0	0.0
			.shstrtab	265	265	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	481887	481887	0	0.0
			.symtab	287248	287248	0	0.0
			.text	496340	496340	0	0.0

[github-actions]

PR #26287: Size comparison from 77d72a8 to f075e83

Full report (1 build for cc32xx)

platform	target	config	section	77d72a8	f075e83	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	602714	602714	0	0.0
			(read/write)	204156	204156	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197568	197568	0	0.0
			.comment	206	206	0	0.0
			.data	1468	1468	0	0.0
			.debug_abbrev	956984	956984	0	0.0
			.debug_aranges	103664	103664	0	0.0
			.debug_frame	350552	350552	0	0.0
			.debug_info	19521972	19521972	0	0.0
			.debug_line	2682751	2682751	0	0.0
			.debug_line_str	513	513	0	0.0
			.debug_loc	33340	33340	0	0.0
			.debug_loclists	1506147	1506147	0	0.0
			.debug_ranges	4984	4984	0	0.0
			.debug_rnglists	96278	96278	0	0.0
			.debug_str	3059490	3059490	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	104250	104250	0	0.0
			.shstrtab	265	265	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	481887	481887	0	0.0
			.symtab	287248	287248	0	0.0
			.text	496340	496340	0	0.0